One of the major problems confronting our society today is the generation of wastes. Landfilling had become the method of choice with the prevailing mentality being "Out of Sight-Out of Mind!" The most commonly considered alternatives to landfills are mass incineration of municipal waste and its related activity, the production of refuse derived fuel (RDF). Incineration and refuse derived fuel produce a variety of pollutants that cause respiratory discomfort and disease. These pollutants are caused by incomplete combustion of municipal solid waste and the combustion of plastics.
It is known that municipal solid waste contains a tremendous amount of materials of value, when recycled. Environmentalist and public officials view the recycling of these materials as the most desirable method of waste disposal; however, present recycling efforts have reduced the volume of MSW by less than ten percent.
In light of the shortcomings, both technically and economically of mass-burn and refuse derived fuel and with an awareness of the wealth of recyclable materials being lost in landfills, a method of easily classifying and separating recyclables is needed.
In my prior U.S. Pat. No. 4342,830, dated Aug. 3, 1982, steam treatment of MSW is disclosed wherein the sterilized and softened organics are forced through perforations upon sudden release of pressure whereby inorganics and certain synthetics, such as metal cans, glass, plastic containers and the like, are left behind. This method included the addition of significant quantities of water to the wastes and thus required substantial energy consumption in the form of steam to heat the water/waste slurry and to force the resultant sterile and softened organics through the perforations in a singular step. The plastics recovered which were suitable for recycling were generally less than 2% of the waste by weight and were generally severely contaminated with softened organics and dirt. The inorganic materials such as ferrous and non-ferrous metals were also similarly contaminated, making these products less desirable for recycling. The glass components were both broken and contaminated.
In my prior U.S. Pat. No. 4,450,495, dated Jun. 10, 1085, steam treatment was again disclosed wherein the amount of water added prior to steam treatment was insignificantly reduced to conserve energy consumed and to reduce the moisture content of the softened organic fraction to in the order of 60% by weight. There was no method of controlling final moisture content of the softened organic fraction; therefore, making final separation more difficult and decreasing the desirability of the plastics, and inorganic recyclables. The internal steam pressure requirements in combination with the resultant temperatures and the necessary period of time it took to cook and sterilize the waste material and soften the organic matter also caused a melting of many of the plastics and significant heat distortion of most other plastics as in the previous U.S. Pat. No. 4,342,830.
Also in my prior U.S. Pat. No. 4,844,351 a method for separation, recovery, and recycling of plastics from municipal solid waste was disclosed wherein mixed wastes including various plastic elements were subjected to mechanical agitation and heat distortion. The waste were introduced into a processing unit having a means for heating and a means for agitating the wastes. By this method, the plastics were recovered as a mixture that may be recycled. The processing unit included an inclined, cylindrical, rotatable vessel having closing members (hatches) at opposite ends thereof. A plurality of spaced plates, inclined in a common plane and secured to the internal shell of the cylinder extending into the interior of the cylinder. The plates were arranged to provide a lifting and mixing action to the waste material; however, because of the arrangement of the plates, only a small degree of mixing of the materials could be accomplished.
The above noted defects of the prior art is overcome by the method and structure of the present invention which provides for twice "extruding" the waste materials in a pressurized, heated container. Such double extrusion process provides shear stresses which substantially "fluidizes" the organic material thus making it more easily separated from the inorganic materials such as glass, metals, etc.